Find people in Yahoo's large directory of email addresses based on name, location, old email address (!) or organization name...
Popular in Europe, XING helps you find and connect to businesses and their people.
Search the directory of ICQ users with numerous criteria to find old and new friends, and their email addresses.
MyFreeEmailSearch aggregates results from other people search engines as well as the web and public databases to find whomever you seek.
You can search PeekYou's profiles for people (and a way to contact them) by name, company or school.
Finding names on the web and connecting the dots with artificial intelligence and natural language interpretation, ZoomInfo.com has assembled a great profile for just about anybody on the net. It does not have email addresses or ways to contact for everybody, though.
yoName will scour social networking sites and blogs for the name, user name or email address you seek — and return somewhat random but potentially useful results.
If you know the person you are looking for has been online for some time, you can try searching this database of people who posted to Usenet from 1991 to 1996.